Marine vehicles typically employ one or more rotating propellers disposed beneath the water line of the vessel for surface vessels or disposed within a portion of the hull of submersible vessels.
Typically, the propellers in submersible systems have been driven by diesel power, steam turbines or electric motors mounted within the hull of a vessel. A propeller shaft extends through the hull to the propeller mounted on the shaft outside the hull. Such systems have the disadvantage of noise and vibration radiating from the rotating components. Also, such systems typically occupy a great deal of the interior hull space. The motor, typically, is a primary source of noise and vibration. The source of such noise in an electric motor is often torque ripple due, for example, to cogging, i.e., variations in magnetic flux that are related to rotor position, reluctance, and the mechanical coupling between the rotor and propeller shaft.